1. Field of the Invention
This invention relates to antenna systems and, in particular, to an antenna system capable of suppressing grating lobes.
2. Description of the Related Art
Radar and other electronic systems often use antenna arrays to transmit and/or receive electronic signals in a particular direction or range of directions. As illustrated in FIG. 1A, such an antenna array 100 may comprise a backplane 101 on which a plurality of antenna elements 102 are disposed in a spaced-apart fashion by a dimension A in an orthogonal grid pattern. The antenna elements 102 may be used to transmit or receive, or both, depending on the implementation. Generally, electromagnetic signals are transmitted from and received by some or all of the antenna elements 102. In radar applications, as illustrated in FIG. 1B, for example, electromagnetic signals (represented by arrows 104) are transmitted from the array 100. Some of the signals encounter an object 106 and a portion of the signals (represented by an arrow 108) is reflected back toward the array 100, where it is received.
FIG. 1C illustrates a typical graphical representation 110 of the electromagnetic signals received by an array, such as the array 100. The electromagnetic signals, e.g., the signals 108, reflected by an object, such as the object 106, appear as a target feature 112 in the representation 110. However, when the elements 102 are spaced apart such that the dimension A is generally equal to or greater than about one-half of the wavelength of the signals being transmitted, signals transmitted from adjacent elements 102 may interfere with one another, resulting in an electromagnetic phenomenon known as a “grating lobe.” Such a grating lobe may appear as an anomalous feature 114 in the representation 110 and may be incorrectly interpreted as signals reflected from an object.
Various approaches have been developed to overcome this problem. For example, multiple transmit/receive cycles may be performed using signals of different frequencies. Typically, the anomalous feature 114 may be disposed in various locations in the representation 110 depending upon the frequency used, or the anomalous feature 114 may disappear from the representation 110 when some frequencies are used. Such approaches require additional time to process the information and, thus, may not be appropriate depending upon the application.
Another approach to reduce the occurrence of anomalous features 114 has been to decrease the spacing between the antenna elements 102, as shown in FIG. 2A. In the illustrated array 200, the antenna elements 102 are disposed on a backplane 201 in a spaced-apart fashion such that a dimension B is less than about one-half of the wavelength of the electromagnetic signals transmitted by the antenna elements 102. FIG. 2B illustrates a graphical representation 202 of signals received by the array 200. In the representation 202, the electromagnetic signals, e.g., the signal 108, reflected by an object, such as the object 106 of FIG. 1B, appear as a target feature 204. However, no anomalous feature, such as the anomalous feature 114 of FIG. 1C, appears in the representation 202.
While the approach illustrated in FIGS. 2A and 2B is generally effective, the cost of the array 200 may be substantially greater than that of the array 100, since more antenna elements 102 are required for a given array area. Further, in general, each of the antenna elements 102 is electrically connected to a transceiver (not shown). As the density of the antenna elements 102, and thus the transceivers, increases, there may be insufficient room to connect the antenna elements 102 to the transceivers or to attach the transceivers to the backplane 201.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.